Technologies using an LED (light emitting diode) as a light source for a projector that projects an image onto a screen such as a liquid crystal projector and a DMD (digital micromirror device) projector are becoming a focus of attention (see Patent Literature 1).
Since LEDs have long service life and high reliability, projectors using LEDs as their light sources have an advantage of having a long service life and high reliability.
However, on the other hand, the luminance of LED light is low for projectors, and it is therefore not easy to obtain an image with sufficient luminance for projectors using LEDs as their light sources.
The amount of light from a light source available to a display panel as projecting light is limited due to the etendue. That is, it is not possible to efficiently use light from the light source as projecting light unless the value of the product of the light-emission area of the light source and the angle of radiation is set to be equal to or below the value of the product of the area of the plane of incidence of the display panel and the acceptance angle determined by the F number of the illuminating optical system.
For a light source using an LED, the light quantity can be increased by increasing its light-emission area, but when the light-emission area increases, the etendue of the light source also increases. Due to limitations of etendue, it is expected that the LED, as a light source for a projector, will increase the light quantity without increasing the light emission area, but increasing the light quantity without increasing the light emission by a light source that uses an LED is difficult to achieve.
There is a light source apparatus using a laser light source and a fluorescent material described in Patent Literature 2 (Japanese Patent No. 4054594) which recognizes as a problem of the related arts that when an LED is used as a light source of a projector, since the light quantity of the LED is low, a plurality of LEDs need to be used and such LEDs are not suitable for miniaturization of an apparatus.
FIG. 1 is a diagram illustrating a schematic configuration of a light source apparatus disclosed in Patent Literature 2.
The light source apparatus includes fluorescent material 1303 disposed at a focal point position of concave reflection mirror 1300, radiates laser light generated by laser light source 1302 onto fluorescent material 1303 through a hole on a central axis of concave reflection mirror 1300 and emits the fluorescence generated as a parallel luminous flux through the concave reflection mirror 1300. A reflection mirror 1304 is provided on the side of anti-laser light source 1302 of fluorescent material 1303 for reflecting laser light that has passed through fluorescent material 1303.